func generatesZip64(t *testing.T, f func(w *Writer)) bool {
	ss := &suffixSaver{keep: 10 << 20}
	w := NewWriter(ss)
	f(w)
	return suffixIsZip64(t, ss)
}

type sizedReaderAt interface {
	io.ReaderAt
	Size() int64
}

func suffixIsZip64(t *testing.T, zip sizedReaderAt) bool {
	d := make([]byte, 1024)
	if _, err := zip.ReadAt(d, zip.Size()-int64(len(d))); err != nil {
		t.Fatalf("ReadAt: %v", err)